1. Field of the Invention
The present invention relates to (aryl) (amino)borane compounds and to a process for their preparation.
2. Description of the Related Art
Arylboronic acids and esters are generally prepared by borylation of aromatic organomagnesium or organolithium derivatives. These methods are expensive, require specific conditions and are not general, which renders them rather unattractive. They have also been prepared by reaction of tetraalkoxydiboron compounds with brominated or iodinated aromatic derivatives in the presence of palladium catalysts (T. Ishiyama et al., J. Org. Chem., 1995, 60, 7508). This method does not involve organomagnesium or organolithium compounds but the preparation of the tetraalkoxydiboron compounds requires the use of molten metallic sodium or potassium at high temperature in highly flammable solvents, which renders the method dangerous. Pinacolborane can react with brominated or iodinated aromatic derivatives in the presence of palladium catalysts to give arylboronic esters of pinacol (M. Murata et al., J. Org. Chem., 1997, 62, 6458). However, pinacolborane, prepared from the borane-dimethyl sulfide complex (Me2S.BH3), is a volatile product used in excess and is not very reactive. The boronic esters obtained are very stable and do not make possible ready refunctionalization around the boron atom.